376 balanidjE. 



variable. It is in the opercular valves, which in other genera 

 offer by far the most reliable character, that we encounter 

 the chief cause of perplexity ; for the characters thus de- 

 rived, though at first appearing very distinct, blend into 

 each other, and are not accompanied by any well marked 

 differences in the shell. Only a few of my specimens have 

 any habitat ; but the geographical range, as far as it does 

 go, throws no light on the question which forms to regard 

 as species and which as varieties. As is generally the 

 case with cirripedes, the variations are local, so that the 

 greater number of specimens imbedded in the same coral 

 resemble each other. Under these circustances I have 

 thought it best, after repeated examinations of a very large 

 suite of specimens, to describe separately each variety, with- 

 out attaching any name to it; but I will first make a few ge- 

 neral remarks on the structure of the shell. If I do not thus 

 throw much light on the subject, I shall at least not burden 

 it with error. I believe that the species will be definitely 

 made out only by persons resident in the coral-bearing 

 zones. I have given copious illustrations of the opercular 

 valves ; for, if my view be correct, this genus offers a curious 

 and striking case of variation ; if, on the other hand, I am 

 wrong, the drawings, I hope, will aid others in coming to 

 a more correct conclusion. 



Creusia spinulosa. PL 13, fig. 6 a — 6/i: PL 14, 6i — 

 6 u, 6 u. 



Creusia spinulosa. Leach (!) Encyclop. Brit. Suppl., vol. 3, 



PI. 57, 1824. 

 Creusie spinuleuse. Be Blainville. Diet. Sc. Nat., PI. 116, fig. 6. 

 Creusia gregaria. G. B. Soicerby (!) Genera of Recent and 



Fossil Shells, No. 18, Sept. 1823. 

 ■ — GRANDis. Chenu. Illust. Conch. Tab. 1, fig. 2, sed non 



fig. 2 a and b. 



llab. — Philippine Archipelago, China, Singapore, Java, Red Sea, West 

 Indies ; imbedded in various corals ; Mus. Brit., Cuming, Stutchbury, 

 Dunker, &c. 



General Appearance. — The shell is oval, generally flat, sometimes 

 conical, with narrow and approximate ridges radiating from the orifice 



